Technical Field
Embodiments of the present invention relate to an image display apparatus and a vehicle provided with the image display apparatus.
Background Art
Image display apparatuses are known in the art that are provided for mobile objects such as vehicles, aircrafts, and ships, and are used by the drivers of these mobile objects to visually recognize useful information for driving or operating the mobile objects. Such image display apparatuses are called heads-up display (HUD). The useful information for driving or operating the mobile objects includes, for example, the information about objects existing in the viewing field of the driver of the mobile object, the information useful for safe and comfortable driving, and an alert to inform the driver of the operational status of the mobile object.
A HUD displays the information as above in the viewing field of a driver as a virtual image. Accordingly, the driver can visually recognize the above information more securely with reduced movement of line of sight. The HUD generates an image indicating the above information as an intermediate image, and projects the generated intermediate image onto an observation optical system to display a virtual image.
Several kinds of method is known in the art for the HUD to generate an intermediate image. For example, a panel system where an intermediate image is formed by an imaging device such as a liquid crystal and a laser scanning system where an intermediate image is formed by scanning a laser beam emitted from a laser diode by a two-dimensional scanning device are known in the art. In the panel system, full-screen light emission is partially blocked to form an intermediate image. In the laser scanning system, each pixel is assigned to either “emitting” pixel or “non-emitting” pixel to form an intermediate image. As known in the art, a laser scanning system can generate an intermediate image with higher contrast than a panel system does.
In the laser scanning system, a microlens array (MLA) may be used to generate an intermediate image. A microlens array is an optical element on which a plurality of minute lenses (microlenses) are arranged at regular intervals. If these microlenses are two-dimensionally scanned by laser beam, interference patterns such as moire and diffraction patterns due to diffracted light that is strengthened in a certain direction may occur on the exit plane side. Such interference patterns or the like may become a factor in reducing the image quality of an intermediate image. In other words, the occurrence of such interference patterns or the like may reduce the viewability of information through a virtual image. As known in the art, the shape of microlenses or the like may be modified in order to prevent the interference patterns as above from occurring (see, for example, JP-2015-169804-A).
Moreover, the pitches of microlenses or the pitches of a scanning line on the microlenses relate to the occurrence of moire due to a MLA. Accordingly, in order to improve the image quality of an intermediate image and the viewability of a virtual image in a HUD with a laser scanning system where a MLA is used, there is further room for improvement in the relation between a scanning line and a microlens array.